BLOOD. 115 



blood cannot hold the corpuscles in suspension. There is 

 then formed, prcAiously to the separation of the fibrin, a layer 

 of yellow plasma above the sunken blood-corpuscles, in which 

 (i. e. in the plasma), upon the subsequent coagulation, a cer- 

 tain quantity of fibrin separates (crusta inflammatoria) . 



In some observations on the blood of a cachectic horse, 

 made during the summer, I found that the corpuscles sunk so 

 rapidly in the tumbler in which the fluid was received, that a 

 layer of plasma was formed, amounting to nearly two thirds 

 of the whole volume of the blood, previously to the coagulation 

 of the fibrin. The fibrin, which was present in large quantity, 

 then began to coagulate, and after some time a solid cylinder 

 of coagulated plasma was formed, which resisted a consider- 

 able degree of pressure, and under which the uncoagulated 

 blood-corpuscles were distributed. 



In some pathological states the blood contains mere traces 

 of fibrin ; in these cases no clot is formed ; we observe merely 

 the separation of a few dark gelatiniform flocciili. 



The coagulation of the plasma is a consequence of the 

 cessation of the vitality of the blood; hence it occui's not 

 merely in blood abstracted from the living body, but after 

 death, and under some peculiar circumstances, in the vessels 

 themselves. It is independent of external influences, for it 

 occurs equally in ordinary aii', in vacuo, and in various gaseous 

 atmospheres. It may be accelerated or impeded by certain 

 agents, and may even be altogether prevented; the blood, 

 however, when prevented from coagulating in this manner, is 

 in a state very diff'erent from that in which it previously existed 

 in the body, the fibrin having undergone a chemical change. 



The retardation or j)revention of coagulation} 



Fresh blood becomes solid below 32°, without the coagula- 

 tion of the fibrin, which however occurs after thawing. 



• [A full account of the various experiments by John Hunter, Da\7, Prater, Scuda- 

 more, and others, on the effects of various agents upon the coagulation of the blood, 

 to the period it was written, may be found in Ancell's seventh lecture " on the Phy- 

 siolog}' and Pathologj' of the Blood." Lancet, 1840.] 



